Applying wind load to a high rise structure

Grasshopper Karamba3D
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1

Hello,
I have been trying to set up an analysis workflow for a high rise structure. I have seen in the tutorial as per the below link, that wind load is only applied to mesh points which are oriented towards the vector of wind. It is also noteworthy that no supporting slabs or core is used here.
https://www.karamba3d.com/tutorials/tutorials_archive/twisted-tower/

There is however also the possibility to apply wind load as a constant mesh load.
Both options produce different results. Which approach is correct?

I am extracting the wind speed and the primary direction from the ladybug windrose component. In order to calculate the wind load per sqm, I am using the formula as described here

I would use the resulting kn/sqm as the amplitude of the vector. Is this the correct approach?

Is there any appropriate example of anaylising a high rise with Karamba besides the 2D examples available on the Karamba page itself?
Best

2

Dear @karamba3d would you be able to help me with this please?

3

Dear @PA_83,
you will get the most realistic results when applying the wind pressure that results from a CFD analysis with e.g. Butterfly via a ‘MeshloadVariable’-component.
Depending on the height of your high-rise, the approach with a constant overall wind-pressure underestimates the effect of wind-loads since wind-speed and thus wind-pressure increase with height. Depending on the type of surrounding geography (alpine region, see-side) the wind-load varies. As a rough estimate you can use a characteristic wind-pressure of w[kN/m²]~0.55*(2+z[m]/100) for heights z between 50 and 150m. The formula can be found in ‘Beton im Hochbau’, A. Pauser, Verlag Bau+Technik, 1998 page 22.
– clemens

4

Dear @karamba3d ,
thanks for your response. I found quite a few methods of applying wind load to structures using Karamba, which is really a bit confusing.
a) In some examples the wind load was applied to all the points of the structure evenly. The kN value of the load was divided by the number of points

b) in another example a generic kN/m2 value is applied to points facing the direction of the wind
https://www.karamba3d.com/tutorials/tutorials_archive/twisted-tower/

I am now applying the formula of w[kN/m²]~0.55(2+z[m]/100)* for a tower of 120 m height.

Another question is, if I must assume supports at the slab? This obvisiouly reduces the displacement to a large extent.

5

Dear @PA_83,
the most practical way for defining wind-loads in Karamba3D depends on what you want to model and how you set up the GH-definition.
Wind-loads are hard to quantify. Therefore one needs to use a safety-factor of 1.5 for converting characteristic values to design values. So excessive precision is out of place in case of wind-loads in the early design stage.
It is certainly a good idea to connect the facade to the slabs in order to reduce displacements.
– Clemens